This is an omnibus project that covers a variety of studies on development, validation, refinement, and applications of methods to determine the basic biochemical and physiological mechanisms underlying the regulation of cerebral blood flow (CBF) and energy metabolism at rest and in response to functional activation of neural pathways. Most of the work in this project during the last year has been directed at identifying the biochemical mechanisms of regulation of CBF and metabolism. Results this year have shown that there are multiple mechanisms operating at different relay stations along a pathway. Adenosine receptors in vascular smooth muscle are involved in the regions of the primary synapses. Adenosine produced by altered energy metabolism during functional activation initiates a cascade of events that act on the adenosine receptors and ends in opening of K+ channels, membrane hyperpolarization, and smooth muscle relaxation in the cerebral blood vessel walls. At higher level stations in multisynaptic pathways nitric oxide (NO) produced by neuronal NO synthase appears to play a role. Neither adenosine nor nitric oxide account fully for the increases in cerebral blood flow evoked by functional activation, and other factors must be involved. Studies in progress indicate that astroglial metabolism may be intimately involved in the regulation of cerebral blood flow Publications Gotoh, J., Itoh, Y., Kuang, T.-Y., Cook, M., Law, M. J., and Sokoloff, L.: Negligible glucose-6-phosphatase activity in cultured astroglia. J. Neurochem. 74: 1400-1408; 2000. Sokoloff, L.: In vivo veritas: Probing brain function through the use of quantitative in vivo biochemical techniques. Ann. Rev. Physiol. 62: 1-24; 2000.Sokoloff, L.: A historical review of developments in the field of cerebral blood flow and metabolism. Proc. of 6th Keio University International Symposium for Life Sciences and Medicine, Ischemic Blood Flow in the Brain. In press Itoh, Y., Law, Mona J., and Sokoloff L.: Effects of the Na+/H+ exchanger monensin on intracellular pH in astroglia. Brain Res. In press. Gotoh, J., Kuang, T-Y, Nakao Y., Cohen, D. M., Melzer P., Itoh Y., Pak, H., Pettigrew, K.,and Sokoloff L. Regional differences in mechanisms of cerebral circulatory response to neuronal activation. Am. J. Physiol.-Heart Circulatory Physiol. In press.